Method of and apparatus for descaling and leveling a metal strip

ABSTRACT

A metal strip is passed continuously through three succeeding roller-tensioning devices. Between the upstream and central tensioning device the strip is elongated by between 0.5 and 1.3 percent so as to descale this strip. Between the central tensioning device and the downstream tensioning device the strip is elongated by between 2 and 2.5 percent so as to level the strip and prevent end bowing thereof.

United States Patent [1 1 [111 3,924,428

Noe [4 Dec. 9, 1975 METHOD OF AND APPARATUS FOR [56] References CitedDESCALING AND LEVELING A METAL I UNITED STATES PATENTS STRIP 2,163,5046/1959 Thomas.... 29/81 A [75] Inventor: Oskar No, Mulheim (Ruhr),3,261,191 7/1966 Wasson 72/161 Germany 3,559,431 2/1971 Noe et a1. 72/83,626,735 12/1971 Lebourg et a]. 72/205 X [73] Assrgnee: Firma BWGBergwerkund @lzwerkMaschinenbau GmbH, Primary Examiner-Milton S. MehrDulsburg, Germany Attorney, Agent, or Firm1(arl F. Ross; Herbert 22Filed: Oct. 7, 1974 'Dubno [21] Appl. No.: 512,604 [57] ABSTRACT A metalstrip is passed continuously through three [30] Forelgn ApphcatlonPnonty Dam succeeding roller-tensioning devices. Between the up- Oct. 8,1973 Germany 2350503 stream and central tensioning device the strip iselongated by between 0.5 and 1.3 percent so as to descale [52] US. Cl.72/40; 29/81 A; 72/ 161; this strip. Between the central tensioningdevice and 3; 6 /3 P the downstream tensioning device the strip is elon-[51] Int. C1. B21B 45/06; B21D 1/04 gated by between 2 and 2.5 percentso as to le el th [58] Field of Search 72/39, 40, 205, 161, 160, stripand prevent end bowing thereof.

4 Claims, 3 Drawing Figures LEVELING 4 O'S'CAL/NG TEQBQ METHOD OF ANDAPPARATUS FoR DESCALING AND LEVELING A MET L STRIP FIELD OF THEINVENTION The present invention relates to a method of and an apparatusfor descaling and leveling a metal strip. More particularly thisinvention concerns a roller-levelerthrough which a metal strip is passedbeforepickling.

BACKGROUND OF THEINVENTION Prior to thepickling of a metal strip, inparticular a steel strip, it is necessary toldescale the strip. This;isdone in a so-called roller-leveler which stretches the sheetlongitudinally to a limited extent while alternately and reverse bendingit soas to remove all ;of the scale thereon. At the same time thestripis flattened 2 The apparatus according to the present inventioncomprises three roller ten'sioners separating two reverse bendingdevices. The strip is descaledbetween the extreme upstream and thecentral roller tensioner and is leveled between the central and theextreme downstream roller tensioner.

BRIEF DESCRIPTION OF THE DRAWING of operation of the system according tothe present in- Experiments have shown that the amount of elongationnecessary to descale the strip adequately does not eliminate lateralbowing, that is a deformation of the strip in its own plane toward oneside caused by hotworking of the strip. This lateral bowing occurs atthe ends of the strip most often so that it is necessary to cut offthese ends before the strip can be further processed, as it isimpossible to pass the strip through conventional treatment apparatuswhen it is bowed in this manner.

It has been suggested that this lateral bowing can be eliminated bystretching the strip longitudinally to a relatively large extent. Atthis high degree of stretch however the descaling is usuallyinsufficient so that the known systems usually employ a degree ofstretch that is a middle ground between the two levels, so that thedescaling is usually inadequate while the lateral bowing is alsoinusfficiently suppressed.

OBJECTS OF THE INVENTION It is therefore an object of the presentinvention to provide an improved method of an apparatus treating a metalstrip.

Another object is the provision of improved system for descaling andleveling a metal strip.

Yet another object is to provide such an apparatus which in one simpleoperation both effectively descales the strip and leveling it perfectly,thereby eliminating any lateral bowing at the ends thereof.

SUMMARY OF THE INVENTION These objects are attained accordingto thepresent invention in a system wherein the strip is passed through a pairof succeeding stretching assemblies. In the upstream assembly the stripis subjected to a relatively low degree of longitudinal elongation,equal to the maximum-descaling stretch (MDS). At the downstream assemblythe extent of stretch is considerably greater so as to completelyeliminate lateral bowing of the strip. Thus in accordance with thepresent invention the strip in a single pass is both completely descaledand perfectly leveled, both of these operations being carried out atlevels which correspond to the ideal stretch for that operation.

In accordance with the present invention the maximum-descaling stretchin the upstream device is between 0.5 percent and 1.3 percent forremoval of scale on the strip.

In accordance with yet another feature of this invention the extent ofstretch in the downward stream assembly serving to level the strip isgreater than 2 percent, advantageously between 2 and 2.5 percent.

vention.

' SPECIFIC DissCRIPIIoN As shown in FIG. 1 a steel strip 1 is passed ina direction 8 through three succeeding roller-tensioners 2a, 2b, and 20each having two respective driven tension rollers 3a, 3b, and 3c.Between the upstream roller assembly 2a and the central roller assembly2b there is provided a reverse-bending device 4 having three reversingrollers 9 much as described in my US. Pat. No. 3,777,532 issued on Dec.11, 1973. Idler rollers 5 are employed to either side of this reversebender 4 for proper feeding of the strip 1.

A similar reverse bender 4" having rollers 9" is provided between thecentral tensioning assembly 2b and the downstream tensioning assembly20. After exiting from the downstream assembly 20 the strip 1 ispickled.

It has been found that a maximum amount of g/m of scales is removed asillustrated in FIG. 2 when the upstream assembly 2a and the centralassembly 2b are so driven as to elongate the strip 1 by an extent equalto the maximum-descaling stretch (MDS) of between 0.5 percent and 1.3percent. Thus the drive motors 10a and 10b for the assemblies 2a and 2bare so controlled that they stretch the strip between these assembliesby approximately 0.8 percent.

Similarly as shown in FIG. 3 it has been found that the lateraldeflection h in mm/m of the strip 1 is reduced greatly when the strip 1is stretched greater than 2 percent. Between 2 and 2.5 percent has beenfound advantageous. To this end the drive motor of the assembly 2c isdriven at a rate relative to the drive speed of the motor 10b of theassembly 2b to stretch the strip 1 between these two assemblies 2b and2c by an extent equal to between 2 percent and 3 percent.

Thus the band section 6 between the upstream assembly 2a and secondassembly 2b is subjected to a longitudinal tension of approximately 10tons while the ;tension on the section 7 between the assembly 2b and theassembly 20 is equal to approximately 20 tons.

The system and apparatus according to the present invention is equallyusable with nonferrous metal sheets. It is also possible to provide inthe system according to the present invention various metal workingmachines between the rolling-tensioning assemblies 2a 20. Four suchassemblies could also be provided as could only two to carry out thepresent invention.

I claim:

1. A method of treating a metal strip comprising the steps of:

longitudinally stretching said strip to a relatively small extentbetween 0.5 and 1.3 percent corre- 3 sponding to maximum-descalingstretch while reverse bending the strip to remove scale from the strip;thereafter longitudinally stretching said strip to a relatively largeextent sufficient'to level said strip; and

pickling said strip after leveling same. 2. The method defined in claim1 wherein said strip is leveled by stretching more than 2 percent.

3. An apparatus for treating a metal strip and comprising:

descaling means for longitudinally stretching said strip to a relativelysmall extent between 0.5 and 1.3 percent to remove scale therefrom;reverse bending means for reverse bending said strip simultaneously withthe longitudinal stretching thereof by said descaling means;

4 leveling means downstream from said descaling means for stretchingsaid strip to a relatively large extent sufficient to level said strip;and

means for pickling said strip downstream of said levcling means.

4. The apparatus defined in claim 3 wherein said descaling meansincludes an upstream roller-tensioner, said leveling means includes adownstream roller-tensioner, and said apparatus includes a centralroller tensioner between said upstream and downstream roller tensioners,an upstream reverse bender being provided between said upstreamroller-tensioner and said central roller-tensioner and a downstreamreverse bender being provided between said central roller-tensioner andsaid downstream roller-tensioner, each of said reverse benders includinga plurality of succeeding and parallel rollers defining a sinusiodalpath for said strip.

1. A method of treating a metal strip comprising the steps of:longitudinally stretching said strip to a relatively small extentbetween 0.5 and 1.3 percent corresponding to maximumdescaling stretchwhile reverse bending the strip to remove scale from the strip;thereafter longitudinally stretching said strip to a relatively largeextent sufficient to level said strip; and pickling said strip afterleveling same.
 2. The method defined in claim 1 wherein said strip isleveled by stretching more than 2 percent.
 3. An apparatus for treatinga metal strip and comprising: descaling means for longitudinallystretching said strip to a relatively small extent between 0.5 and 1.3percent to remove scale therefrom; reverse bending means for reversebending said strip simultaneously with the longitudinal stretchingthereof by said descaling means; leveling means downstream from saiddescaling means for stretching said strip to a relatively large extentsufficient to level said strip; and means for pickling said stripdownstream of said leveling means.
 4. The apparatus defined in claim 3wherein said descaling means includes an upstream roller-tensioner, saidleveling means includes a downstream roller-tensioner, and saidapparatus includes a central roller tensioner between said upstream anddownstream roller tensioners, an upstream reverse bender being providedbetween said upstream roller-tensioner and said central roller-tensionerand a downstream reverse bender being provided between said centralroller-tensioner and said downstream roller-tensioner, each of saidreverse benders including a plurality of succeeding and parallel rollersdefining a sinusiodal path for said strip.